This invention relates to a process for expanding tobacco to increase its filling capacity, i.e., to reduce its bulk density. The process is especially suitable for treating cigarette cut filler.
During curing, the tobacco leaf loses moisture and shrinks and subsequent storage and treatment, such as cutting, contribute to this shrunken or collapsed condition of the entire leaf, particularly the thin lamina portion which is used for cut filler.
Prior to about 1970, several processes have been suggested or proposed for increasing the filling capacity of tobacco. Insofar as we are aware, none of these proposals were sufficiently practical to be put into commercial production and use. Many did not achieve enough expansion or increase in filling capacity to be economically practical; others created too many fines or otherwise damaged the fragile lamina, while others were applicable only to the easily expanded stem portion of the tobacco leaf and were not applicable to lamina, the principal ingredient of cut filler for cigarettes. Still other suggestions, such as freeze drying, required elaborate and expensive processing equipment and very substantial operating costs.
For example, U.S. Pat. No. 1,789,435 to W. J. Hawkins describes a method and apparatus for increasing the volume of cured tobacco which has undergone shrinkage during curing. In this process, cured and conditioned tobacco is contacted with a gas, which may be air, carbon dioxide or steam, under about 1.4 Kg/cm.sup.2 pressure and then the pressure is suddenly released to expand the tobacco constituents toward their original volume. It is stated in this patent that the volume of tobacco may, by that process, be increased by about 5-15%.
A series of patents to Roger Z. de la Burde, U.S. Pat. Nos., 3,409,022; 3,409,023; 3,409,027; and 3,409,028, relate to various processes for enhancing the utility of tobacco stems for use in smoking products by subjecting the stems to expansion operations utilizing various types of heat treatment or microwave energy. Processes for expanding tobacco stems are not particularly relevant, however, because stems are so easily puffed.
U.S. Pat. No. 3,710,802 to William H. Johnson and British Specification No. 1,293,735 to American Brands, Inc., relate to freeze-drying methods for expanding tobacco.
None of these processes have proved to be practical for expanding cut filler.
In 1970, Fredrickson U.S. Pat. No. 3,524,451 (reissued as Re. 30,693 in 1981) and Moser-Stewart U.S. Pat. No. 3,524,452 were granted. These patents describe processes wherein tobacco is contacted with a volatile impregnant and then heated by rapidly passing a stream of hot gas in contact therewith to volatilize the impregnant and expand the tobacco. These flash-expansion processes proved to be the first commercially practical processes for increasing the filling capacity of tobacco, particularly cut filler, and have now been widely accepted and put into extensive commercial use throughout the world.
A variation of these processes is described in the subsequently issued Fredrickson-Hickman U.S. Pat. No. 3,683,937 which teaches increasing the filling capacity of tobacco by contacting it with vapors of a volatile impregnant while maintaining the temperature of the tobacco above the boiling point of the impregnant at the prevailing pressure so that the tobacco remains free of any liquid or solid form of the impregnant, and thereafter rapidly reducing the pressure or rapidly increasing the temperature to provide vapor releasing conditions and expansion of the tobacco.
Armstrong U.S. Pat. No. 3,771,533 involves a treatment of tobacco with carbon dioxide and ammonia gases to form ammonium carbonate in situ. The ammonium carbonate is thereafter decomposed by heat to release the gases within the tobacco cells to cause expansion of the tobacco.
More recently, Utsch U.S. Pat. Nos. 4,235,250, Burde, et al., 4,258,729, and Sykes, et al., 4,336,814 disclose the use of a particular impregnant, carbon dioxide, as the expansion agent in processes wherein the tobacco is contacted with carbon dioxide gas or liquid to impregnate the tobacco, and thereafter the carbon dioxide-impregnated tobacco is subjected to rapid heating conditions to volatilize the carbon dioxide and thereby expand the tobacco.
Insofar as we are aware, all of the processes for increasing filling capacity of tobacco which have been used commercially require a heating step to volatilize the impregnating material which is costly in energy expenditure and equipment needed.
The primary object of this invention is to provide a process for increasing the filling capacity of tobacco wherein no heating step is needed to volatilize the impregnating material for expanding the tobacco cellular structure.